To practice corneal ablation, an excimer laser with wavelength of 193 nm has been recently developed. Photorefractive keratectomy has been also investigated and utilized for corneal refractive correction. Phototherapeutic keratectomy, such as corneal leukoma, pterygium, corneal erosion and herpetic keratitis surgeries, can also be performed using the excimer laser. The excimer laser is also used for penetrating and lamellar keratoplasty.
Prior to the excimer photoablation to sculpt corneal stroma, the epithelium of the cornea to be treated is removed manually with a spatula. Prior to the corneal surgery, at least one of the following ophthalmic solutions are administered: antibiotics, miotics, midriatics or anesthetics.
When a lid retractor, which is used to secure the eyelid open, depresses the eyeball, the administered ophthalmic solution is unexpectedly exuded onto the corneal surface along with tears. Such exudation is eliminated by manually applying a conventional sponge or using a drainage tube attached to the temporal lid margin for continuous outflow of the exuded fluids.
This exudation on the cornea interferes with treatment because it reflects some light back into the microscope while absorbing some of the laser's light, thus making corneal ablation less effective.
In order to remove such exuded fluids from the cornea, a stick-type polymeric absorbent, a gauze or drain tubing is used. However, these techniques do not sufficiently or conveniently remove a sudden increase in the amount of exuded fluid, particularly during laser therapy.
As the excimer laser heats the corneal tissue, it causes more inflammatory responses and changes the corneal thickness resulting in a postoperative corneal haze. The patient must, therefore, begin a corticosteroids regimen after the laser surgery to minimize corneal inflammatory response which causes corneal haze.
It is reported that topical steroid use over a few months is potentially hazardous.
Accurate axis alignment is required in excimer laser astigmatism correction to achieve optimal results, and is mandatory in any corneal surgery.
The annular sponge appearing in page 42 and 43 in Excimer Laser Surgery, published by Igaku-Shoin Medical Publishers, Inc., New York, is exemplary of prior laser ablation. The annular sponge is placed on the outside of the cornea, because the cornea has to be "marked" for subsequent procedures. The annular sponge is soaked in a topical anesthetic and placed on the eye for marking the center of the pupil by a hook and is removed after the marking is made. An annular sponge used only for anesthesia has a long arm for easier manipulation of the sponge.